1. Field of the Invention
The present invention relates to a technique for detecting a moving object in a passage.
2. Description of the Related Art
Various techniques have conventionally been proposed for detecting a moving object such as a person in a passage. For example, the following technique has been known for detecting the moving object. Specifically, a slit light beam is irradiated to a predetermined monitoring line, which serves as a subject to be irradiated, along a widthwise direction of the passage, whereupon the vicinity of the monitoring line is repeatedly image-captured at a predetermined time cycle to thereby obtain an image. Then, an image of the slit light beam appearing in the image as an emission line is analyzed to detect the moving object (for example, Japanese Unexamined Patent Publication No. 8-161453, and Japanese Unexamined Patent Publication No. 2001-505006 which is an equivalent to U.S. Pat. No. 6,600,509).
In the above-mentioned detecting technique, when the slit light beam is blocked by the moving object at some position on the monitoring line, a pixel value in the image corresponding to this position is reduced compared to a non-blocked state. Therefore, a difference between a reference value when the slit light beam is non-blocked and the actual pixel value is obtained, and if this difference value is not less than a predetermined judgment threshold value, it can be judged that the slit light beam at the position corresponding to the pixel is blocked. Consequently, a moving object can be detected by considering that a moving object is present at the position where “the slit light beam is judged to be blocked” by this judgment.
However, the slit light beam is reflected on not only the floor surface of the passage but also the surface of the moving object. Therefore, there may be a case where the pixel value corresponding to the blocked state of the slit light beam is increased to approximately the same level as that of the reference value by the reflected light of the slit light beam from the surface of the moving object, depending upon the height or reflectivity of the moving object. In this case, whether the slit light beam is blocked or non-blocked cannot accurately be judged, thereby deteriorating the judging precision.
Further, the judgment threshold value is, in general, the same at all positions on the monitoring line. However, the irradiation intensity of the slit light beam may frequently be non-uniform on the monitoring line. Therefore, whether the slit light beam is blocked or non-blocked cannot accurately be judged depending upon the position on the monitoring line, thereby deteriorating the judging precision.